This invention relates to a temperature-controlled fluid coupling for intermittently driving a cooling fan attached to an automotive engine or similar equipment.
U.S. Pat. No. 4,662,495 (Brunken) discloses a typical design of a temperature-controlled fluid friction coupling. According to this design, a housing is rotatably supported on a drive input shaft adapted to connect with an internal combustion engine. The interior space of the housing is separated by a partition into a reservoir chamber and a fluid working chamber. On the drive input shaft, a rotor is fixed so as to form mutually opposite shearing gaps between the housing and the rotor. A radiator cooling fan is mounted on the housing. To the outer surface of the housing, is mounted a temperature sensitive element made of a bimetallic plate which curves in response a change of ambient temperature. In the partition, is provided a valve opening which is opened, narrowed and closed by an actuating pin contacting with the bimetallic plate. As the bimetallic plate is deformed by a change of the ambient temperature, the actuating pin is operated to open, narrow or close the valve opening. Then, viscous fluid flows into or out of the shearing gaps to effect or break a torque transmitting function.
The temperature sensed by the temperature sensitive element is generally the temperature of air coming from an internal combustion engine radiator. For example, at a temperature below a predetermined value, such as 60 degrees centigrade, the bimetal plate is kept on a flat configuration, so that the valve lever closes the valve opening permitting the coupling to be in a disengaged condition (OFF). On the other hand, if the temperature rises beyond 60 degrees centigrade, the bimetal plate is bent into a curved configuration, so that the valve lever leaves the valve opening permitting the coupling to be in an engaged condition (ON).
In the prior art, the valve lever is generally made by an elongated flat plate and the free end thereof moves along the axial direction of the coupling thereby opening and closing the valve opening arranged in the partition.
However, this type of axially contacting and separating movement cannot provide a stable performance. For example, at the moment when the open area of the valve opening approaches a small limit, the valve lever tends to be attracted or stuck to the partition. On the other hand, at the moment when the open area of the valve opening approaches a large limit, the valve lever tends to be over-deflected leaving far from the partition. These undesirable phenomena are well known as xe2x80x9chuntingxe2x80x9d which means an irregular rotation or fluctuation of a fan rotation speed.
It is an object of the present invention to provide a fluid coupling for eliminating the irregular rotation due to hunting.
Another object of the present invention is to provide a precise operation of the valve opening, narrowing and closing functions.
Still another object of the present invention is to provide a high performance more sensitive to the temperature and more controllable in a wide range.
According to the present invention, there is provided a temperature-controlled fluid friction coupling for intermittently driving a cooling fan of an internal combustion engine. This coupling comprises a drive input shaft having a disk rotor thereon, a housing rotatably supported on the drive input shaft for supporting a cooling fan, a partition for dividing an interior space of the housing into a torque transmitting chamber and a reservoir chamber, a valve lever for opening and closing a valve opening arranged in the partition, a temperature sensitive element disposed outside of the cover, and an actuating pin extending through a guide hole arranged in the cover.
The housing includes a body and a cover. One end of the actuating pin contacts with the temperature sensitive element, and the other end of the actuating pin contacts with the valve lever.
The actuating pin is arranged movable in a direction parallel to the surface of the partition. The valve lever contacts with the actuating pin near the root end thereof, and the swing end of the valve lever is arranged slidably movable keeping in touch with the surface of the partition having the valve opening therein by reason of its inherent tension.
Thus, in response to a deformation of the temperature sensitive member caused by a change of ambient temperature, the actuating pin moves in a direction parallel to the surface of the partition, so that the swing end of the valve lever moves parallel to the surface of the partition keeping in touch with the surface for changing the open area of the valve opening, thereby controlling the fluid flow from the reservoir chamber to the torque transmitting chamber.
Based upon the above construction, the swing type valve lever of the present invention is not moved along the axial direction of the coupling, but is slidably moved along the circumferential direction of the coupling keeping in touch with the surface of the partition for opening and closing the valve opening. Thus, the valve performance is kept in a stable condition without an irregular rotation due to hunting.
Since the valve lever swings about a pivot near the root end thereof, it becomes possible to enlarge a leverage (power of a lever) of a linkage mechanism between the temperature sensitive element and the valve lever, so that a more temperature sensitive control becomes available.
As a still further advantage, in case that the temperature sensitive element is made by a rectangular bimetallic plate, prior bimetallic plates tend to be heated by radiation from the cover because they are arranged parallel to the surface of the cover. On the other hand, the bimetallic plate of the present invention is arranged perpendicularly to the cover, so that it can clear the radiation, thereby upgrading its sensitivity.
The temperature sensitive control mechanism in the present invention can be modified in miscellaneous arrangements.